The field of wireless communications has seen a rapid evolution in the past, especially during the last two decades. During this evolution, a number of wireless communications standards were introduced, each new standard typically exploiting technological progress in order to offer superior performance. For example, the GSM (Global System for Mobile communications) standard, the EDGE (Enhanced Data rate for GSM Evolution) standard, and the CDMA (Code Division Multiple Access) standard were and still are widely used by wireless communication networks and their subscribers. While early mobile stations such as cellular phones typically supported a single wireless communication standard only, subscribers were quick to demand more versatile mobile stations or devices which can be used with wireless networks operating under different wireless communication standards.
Industrial standards are typically the result of a collaboration of several companies, standard-setting organizations, service providers, and other interested parties. For example, a collaboration between groups of telecommunications associations have founded the 3rd Generation Partnership Project (3GPP). The 3GPP is aimed at making a globally applicable third-generation (3G) mobile phone system specification within the scope of the International Mobile Telecommunications-2000 Project of the International Telecommunication Union (ITU).
Depending on the standard(s) (e.g. GSM, WCDMA) under which a mobile device is intended to operate, the 3GPP requirements define very stringent limits for certain operating parameters of mobile devices, such as cellular phones.
One of the most important transmit parameters which must virtually always be calibrated is the output power of the mobile device. Especially for output power levels and/or output power changes, the 3GPP requirements define very stringent limits. These stringent limits typically require a dedicated and individual calibration of the output power of a mobile device.
Hence, each mobile device typically needs to be calibrated during production. The main goal of factory calibration is to determine and set normalized settings for all parameters which are important for standard-compliance (e.g. 3GPP) and/or basic function of a mobile device and which show a non-predictable variation over production.